Broadly speaking, aerosol spray devices comprise a container holding a liquid to be discharged together and an outlet nozzle associated with a valving arrangement which is selectively operable to allow discharge of the liquid as a spray from the nozzle by means of the propellant provided within the container.
Both “compressed gas propellant aerosols” and “liquefied gas propellant aerosols” are known. The former incorporate a propellant which is a gas at 25° C. and a pressure of at least 50 bar (e.g. nitrogen, carbon dioxide or air). On opening of the valving arrangement, the compressed gas “pushes” liquid in the spray device through the aforementioned nozzle that provides for atomisation. There are, in fact, two types of “compressed gas propellant aerosols”. In one type, only liquid from the container (“pushed-out” by the compressed gas) is supplied to the outlet nozzle. In the other principal type, a portion of the propellant gas from the container is bled into the liquid being supplied to the nozzle which atomises the resulting two-phase, bubble-laden (“bubbly”) flow to produce the spray. This latter format can produce finer sprays than the former.
In contrast, “liquefied gas propellant aerosols” use a propellant present as both a gas phase and a liquefied phase which is miscible within the liquid in the container. The propellant may, for example, be butane, propane or a mixture thereof. On discharge, the gas phase propellant “propels” the liquid in container (including dissolved, liquid phase propellant through the nozzle).
It is well known that “liquefied gas propellant aerosols” are capable of producing finer sprays than “compressed gas propellant aerosols”. This is due to the fact that, in the former, a large proportion of the liquefied gas “flash vaporises” during discharge of liquid from the aerosol spray device and this rapid expansion gives rise to a fine spray. Such fine sprays cannot generally be achieved with “compressed gas propellant aerosols”, in either of the two principal formats described above.
In spite of the fact that conventional “liquefied gas propellant aerosols” are able to produce finer sprays than their “compressed gas” counterparts, we consider there to be a general need for improving the spray discharge characteristics (particularly with regard to “fineness” of spray) of aerosol spray devices, whether they be of the “compressed gas propellant” or “liquefied gas propellant” type. The present invention seeks to address this need.